While a doctoral student at Princeton University in 1957, studying under a founder of theoretical computer science, Raymond Smullyan would occasionally visit New York City. On one of these visits, he met a “very charming lady musician” and, on their first date, Smullyan, an incorrigible flirt, proceeded very logically—and sneakily.
“Would you please do me a favor?” he asked her. “I am to make a statement. If the statement is true, would you give me your autograph?”
Content to play along, she replied, “I don’t see why not.”
“If the statement is false,” he went on, “you don’t give me your autograph.”
His statement was: “You’ll give me neither your autograph nor a kiss.”
It takes a moment, but the cleverness of Smullyan’s ploy eventually becomes clear.
A truthful statement gets him her autograph, as they agreed. But Smullyan’s statement, supposing it’s true, leads to contradiction: It rules out giving an autograph. That makes Smullyan’s statement false. And if Smullyan’s statement is false, then the charming lady musician will give him either an autograph or a kiss. Now you see the trap: She has already agreed not to reward a false statement with an autograph.
With logic, Smullyan turned a false statement into a kiss. (And into a beautiful romance: The two would eventually marry.)
It is this sort of logical playfulness that Smullyan loves, and that everyone seems to love him for. His books on the subjects of recreational math and logic, with titles like What Is the Name of This Book? and To Mock a Mockingbird, not only encouraged people to pursue careers in these topics but also changed how math and logic are taught. Over his near century of life, Smullyan, 96, became an accomplished pianist and magician, made fundamental contributions to modern logic, and wrote about Taoist philosophy and chess. “He is the undisputed master of logical puzzles,” Bruce Horowitz, one of his former Ph.D. students, has said.
posted by f. sheikh